This invention concerns a rock drill bit with chisel-shaped inserts placed in gun-drilled holes of the rock drill bit. The center line of each insert when inserted into the hole inclines an angle .phi. relative to the center line of the rock drill bit and the guiding surface of each insert generally coinciding with the jacket surface of the bit body extends partly on both sides of the plane of front surface of the bit. The cutting edge of each insert is arranged axially outside said plane.
Hitherto known rock drill bits have inserts in holes that emerges only into the front surface and that in some cases inclines relative to the center line of the bit. Known inserts with a rectangular shape having a center line parallel with the center line of the bit has a disadvantage, common with the first-mentioned inserts, in that they tend to bore in an inclined manner. Rock drill bits having conventional inserts in the periphery cause an unstable drilling operation due to the shape of the inserts so that the bores get inclined in the longitudinal direction. Bits provided with rectangular inserts also cause inclined bores as the periphery of the bit only can receive a small number of inserts due to that the brazing process demands a lot of material around each insert and therefore a small number of guiding points are achieved. Only a few regrindings of the inserts may be done and yet obtaining a bore with an acceptable diameter.
The object of the present invention is to provide an improved rock drill bit that solves the above-mentioned problems.